Abstract
In order to determine the extent of the placental transfer of Lithium ion, pregnant rabbits at $27{\sim}29$ days of gestation, which has hemochorial placenta similar to the human placenta, received 2 mM/Kg of $Li^+$ in the form of LiCl intravenously. Maternal arterial blood, placental sinus blood, fetal blood, amniotic fluid and maternal urine were drawn two hours after the single dose of LiCl. Concentrations of $Li^+$, $Na^+$, $K^+$ and osmolarity were measured in plasma of collected bloods, amniotic fluid and urine. Followings are the results obtained. 1) Evident level of $Li^+$ was detected in fetal blood, although fetal plasma concentration of $Li^+$ found to be almost one third of maternal plasma. 2) Plasma concentration of $Li^+$ in placental sinus blood was higher than that in fetal plasma but lower than that in maternal plasma. It means that downward concentration gradient of $Li^+$ from mother to fetus was still remarkable two hours after the injection. 3) Significant level of $Li^+$ was also detected in amniotic fluid. It seemed likely that $Li^+$, at least in part, excreted by the fetal urinary tract. 4) There were no differences in $Na^+$ and osmolar concentration between fetal and maternal blood. 5) From above results, it was concluded that $Li^+$ may transfer across the placenta but limited passage capacity through placental barrier for $Li^+$ is significant, beacause net transfer assumed to be going on even at two hours, at which time maternal equlibrium has been reached.